GRB 221021A

The Fermi GBM team reports the detection of a likely LONG GRB

At 09:18:25 UT on 21 Oct 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221021A (trigger 688036710.740176 / 221021388).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 218.7, Dec = -68.6 (J2000 degrees, equivalent to J2000 14h 34m, -68d 35'), with a statistical uncertainty of 11.9 degrees.

The angle from the Fermi LAT boresight is 132.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221021388/quicklook/glg_skymap_all_bn221021388.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221021388/quicklook/glg_healpix_all_bn221021388.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221021388/quicklook/glg_lc_medres34_bn221021388.gif

Gayathri Raman (PSU), Aaron Tohuvavohu (U Toronto), James DeLaunay
(UAlabama), Jamie A. Kennea (PSU), Tyler Parsotan (GSFC/UMBC) report:

Swift/BAT did not localize GRB 220924A onboard (T0:
2022-09-24T21:44:54 UTC, Fermi/GBM GCN 32812
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 , GECAM trig #35).

The Fermi and GECAM notices, distributed in near real-time, triggered
the Swift Mission Operations Center operated Gamma-ray Urgent Archiver
for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).

Upon trigger by this notice, GUANO sent a command to the Swift Burst
Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from
[-50,+150] seconds around the time of the burst. All the requested
event mode data was delivered to the ground.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu,
arXiv:2111.01769
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 ), detects the burst with a sqrt(TS) of 20.7 in a
16.384 s analysis time bin.

NITRATES results are consistent with a burst coming from outside the
FOV, with DeltaLLHOut of 0.3.

See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.

A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/

E. Bissaldi (Politecnico and INFN Bari) and
C. Meegan (UAH) report on behalf of the Fermi GBM Team:


"At 09:18:25.74 UT on 21 October 2022,
the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 221021A
(trigger 688036710 / 221021388),
which was also detected by the Swift/BAT-GUANO
(Raman et al. 2022, GCN 32817
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 ).

The GBM position is reported in the Fermi-GBM
Final Real-time Localization (GCN 32812
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 ).
The angle from the Fermi LAT boresight
at the GBM trigger time is 132 degrees.

The GBM light curve shows a multipeaked emission
with a duration (T90) of about 68 s (50-300 keV).
The time-averaged spectrum from T0 to T0+60 s is
best fit by a power law function with an exponential
high-energy cutoff.
The power law index is -1.16 +/- 0.03 and the cutoff
energy, parameterized as Epeak, is 2000 +/- 210 keV.

The event fluence (10-1000 keV) in this time interval is
(3.06 +/- 0.07)E-05 erg/cm^2.
The 1-sec peak photon flux measured
starting from T0+34 s in the 10-1000 keV band
is 9.1 +/- 0.5 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"